Excited state refraction of C₇₀/toluene studied by using 4f coherent imaging system with phase object

Dynamic nonlinearities of C₇₀/toluene solution are measured and analysed by an improved picosecond time-resolved pump-probe system based on a nonlinear imaging technique with phase object. The photophysical parameters are determined by the five-level model, which is adopted to interpret the experimental data. The change of refraction index per unit density of the excited state obtained by a numerically simulation is a critical factor to determine the nonlinear behaviour of C₇₀ in picosecond time regime.